Method and device for electrochemical machining of substrates

ABSTRACT

A method and a device with the aid of which a substrate is electrochemically machined, material being removed from the surface of a conductive substrate with the aid of an also conductive tool. The removal takes place as a function of the surface structure which is incorporated into the tool. The core of the present invention is that the substrate and the tool are moved toward one another during the electrochemical etching process. However, it may alternatively also be provided that either the substrate or the tool is locally stationary, while only the counterpart is moved. In a particularly preferred embodiment of the present invention, only the tool is moved toward the substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and a device for electrochemical machining of substrates.

2. Description of Related Art

An electrochemical method for metal machining is known from DE 103 18 732 A1 in which a workpiece to be machined is placed into an electrolyte between two electrodes. The workpiece is machined by applying a voltage to the electrodes which causes material to be removed from the workpiece.

Machining of large surfaces of semiconductor discs is also possible using an electrochemical method. A device suitable for this is shown in DE 102 35 020 A1. The entire etching trough is rotatable about an axis in order to be able to carry out tilting movements.

A method for processing a metallic substrate surface is known from DE 10 2006 030 323 A1. A tool having a solid, ion-conductive material is brought into contact with the metallic substrate surface. If an electrical potential is applied between the substrate surface and the tool, the metal ions of the areas where the tool comes in contact with the substrate surface may be removed from the substrate surface by the tool.

SUMMARY OF THE INVENTION

The present invention describes a method and a device with the aid of which a substrate is machined electrochemically, material being removed from the surface of a conductive substrate with the aid of a likewise conductive tool. The removal takes place here as a function of the surface structure which is incorporated into the tool. The core of the present invention is that the substrate and the tool are moved toward one another during the electrochemical etching process. However, it may also alternatively be provided that either the substrate or the tool is locally fixed while only the counterpiece is moved. In a particularly preferred embodiment of the present invention, only the tool is moved toward the substrate.

Due to the movement, the material removal from the substrate may advantageously be controlled in a targeted manner in that the distance between the surface structure of the tool and the recess created in the substrate by the removal is reduced. In addition, a more or less sharp (lateral) imaging of the surface structure on the substrate is possible due to the controlled movement in that the time for the local removal is controlled. For example, in the event of a longer action, a larger lateral area is etched.

Furthermore, due to the surface structure on the tool, a structured and targeted material removal may be achieved. It is particularly advantageous that controlling the tool movement relative to the substrate enables a material removal largely perpendicular to the substrate surface.

It is also particularly advantageous that by removing the substrate material in a targeted manner a separation of the substrate may take place. By suitably structuring the tool's surface, the substrate may simultaneously be separated into a plurality of sub-substrates. This may be accomplished by etching the substrate completely through from the front side to the rear side.

In one particular embodiment of the present invention it is provided that initially a plurality of sensor elements is produced on or applied to the substrate before the material is removed. The material may be removed directly on the side of the substrate opposite to the sensor elements or may also deliberately recess or enclose the area of the sensor elements.

For producing suitable recesses in the substrate, it is provided to furnish the surface structure of the tool with protrusions and recesses, the material removal from the substrate taking place essentially in the area of the protrusions. For etching the substrate completely through it is necessary that the recesses have at least a depth which corresponds to the thickness of the substrate.

For producing deep recesses it is provided that the tool, in particular with its protrusions, is inserted into the recesses in the substrate produced by the material removal. The etching conditions on the bottom of the recess may advantageously be maintained in order to produce deep holes.

To control the etching conditions or to keep them constant, it may be provided to vary the current and/or the concentration of the electrolyte as a function of the distance between the tool and the substrate. An adaptation of the etching conditions is advantageous in order to advance the material removal from the bottom of the holes, particularly when producing deep holes in the substrate.

In one particular embodiment of the present invention it is provided that the substrate is used as the first electrode and the tool is used as the second electrode for the electrochemical etching process. For this purpose, both parts are connected directly to the electric voltage supply, for example.

It is generally provided that the substrate and the tool have no direct contact during the etching process. If, in contrast, there were a contact at spots between the substrate and the tool, there would be a current flow at this spot whereby the electrolysis would be stopped. However, in order to enable a large-area and uniform removal, attention must be paid that the substrate and the tool do not have any direct (electrical) contact.

Overall, the present invention allows for a shortening of the etching process since it is possible to machine the substrate over a large area. It is thus possible, for example, to produce a plurality of elements from the substrate at the same time by simultaneous separation. This separation also eliminates the previous separation methods such as sawing, which creates shavings or metal spatter which could damage the thin layer or the sensor or circuit elements situated on the substrate. Moreover, no mechanical stress is transferred to the substrate by the etching process so that no individual components are deformed by the separation process. Furthermore, little heat is input into the substrate by the etching process so that the thin layers or sensor elements or circuit elements situated on the substrate are less stressed. Finally, the etching process makes it possible to produce a higher surface quality since the material is removed more homogeneously compared to sawing or drilling processes.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1 a and 1 b show as an example a tool for separating a substrate in a top view and a sectional view.

FIGS. 2 a through 2 f show the method according to the present invention for separating a substrate with the aid of an electrochemical etching process.

FIG. 3 shows a sensor element which may be produced using the method according to the present invention which is described in

FIGS. 4 a through 4 d show the formation of a cavity via the material removal of an electrochemical etching process.

DETAILED DESCRIPTION OF THE INVENTION

In a first exemplary embodiment it is provided to separate thin layer elements or sensors or circuit components, which are produced on a panel-like substrate board, with the aid of the method according to the present invention and a device suitable for this purpose. The separation is so far typically carried out using a sawing, scoring or a laser cutting process in which the produced thin layer elements may be damaged or contaminated by cutting waste such as shavings or metal spatter. In addition, using the above-mentioned processes, the individual separated structures must be removed one by one so that such a separation is very time-consuming.

Using the present invention, a substrate may be divided on a large area by using an electrochemical etching process which machines all separation cuts simultaneously. For this purpose it is necessary that both the tool and the substrate are electrically conductive. As an example, FIG. 1 a shows a top view onto such a tool 100 which has a surface structure 130. In the cross-section along AA′ it is clearly apparent that the round recesses pass through the entire tool.

However, another shape is, of course, also conceivable instead of a round design of the recesses, such as an oval or square design.

In addition, it is also possible to not etch the recess all the way through the tool. The recesses may also be closed on one side of the tool as long as the recesses are able to accommodate the substrate completely.

FIGS. 2 a through 2 f schematically show a method in which a substrate 120 is separated from rear side 150 into individual sections with the aid of a tool 100. Structuring of the tool according to FIG. 1 a may be used to separate round elements from the substrate. These round elements, which have thin layers, sensor elements or also circuit parts on front side 140, may subsequently be processed separately.

Substrate 120, e.g., a steel plate, and tool 100 are initially placed into an electrolyte in which the etching process occurs. For starting the electrochemical etching process, a voltage is applied to the substrate and the tool so that the substrate material may be locally electrochemically removed. As illustrated in FIG. 2 a, the substrate and the tool are initially placed at a certain distance from one another. After the voltage is applied, the two parts move closer. This takes place advantageously in that the substrate is stationary while the tool is moved toward the substrate. However, it is also possible that only the substrate is moved or also both parts are moved.

As is apparent from FIGS. 2 b through 2 d, material is removed from substrate 120 at those points at which the tool has elevations or protrusions and has thus a smaller distance to the substrate so that the material removal is the greatest at those points. The tool is subsequently inserted into the holes or recesses produced in the substrate in this way.

The etching process and thus the separation is terminated when substrate 120 has been etched completely through, i.e., when the protrusions of tool 100 have completely penetrated thickness 160 of substrate 120 (see FIG. 2 d). Thereupon, the tool is moved back into the starting position so that the separated components of the substrate may be removed and processed further.

In a second exemplary embodiment, the method according to the present invention is used for producing sensor elements as illustrated in FIG. 3. The sensor element has a thin layer 320 on front side 440 of a substrate 300 with the aid of which circuit elements or piezoresistive resistors may be implemented. By introducing a cavity 360 from the rear side, a diaphragm 310 may be produced on the front side of the sensor element. If the diaphragm is deformed by applying pressure, a pressure may be detected via the piezoelectric resistors. The separation cuts are shown using dashed lines 350 which are necessary when sensor elements of this type are produced, i.e., on a large area on a panel-like substrate, using steel, for example.

While cavities in metal or steel substrates are typically produced using drilling, turning, or milling processes, the cavity is formed according to the present method via the material removal of an electrochemical etching process. A suitable thin layer is initially applied to front side 440 of substrate 420 which contains piezoelectric resistors and/or (evaluation) circuit elements, for example. A plurality of cavities 460 is subsequently etched from rear side 450 of substrate 420 as FIGS. 4 a through 4 d show, thereby forming diaphragms 410 which are underneath the applied thin layer. However, it is also conceivable that cavities 460 are first produced in the substrate and the thin layer is only subsequently applied.

As already described in connection with the separation of the first exemplary embodiment, substrate 420 and tool 400 are initially placed into an electrolyte solution at a certain distance for producing the cavities (see FIG. 4 a). After the substrate and the tool are connected to an electrical voltage source, the electrochemical etching process is started. Due to the electromagnetic fields created thereby, the greatest material removal takes place at those points which have the smallest distance between the substrate and the tool. However, in order to obtain a targeted material removal it is necessary to move the tool having protrusions 470 toward the substrate (see FIG. 4 b). Due to this movement, a recess is produced in the substrate which forms a cavity 460 if protrusions 470 are suitably designed. In contrast to the previously described separation method, it is not provided to etch the substrate through its entire thickness for producing diaphragm 410 in the sensor element. In fact, the etching process is selectively aborted when the intended diaphragm thickness is reached (see FIG. 4 c). After tool 400 is moved back, a substrate 420 is thus obtained which has a plurality of cavities 460 which is etched simultaneously. For separating the individual sensor elements, a conventional separation method may subsequently be applied using a saw, a milling machine, or a laser. However, it is more advantageous to use a separation method according to the first exemplary embodiment. For this purpose, tool 400 is merely to be exchanged for a suitable tool 100 and adjusted to substrate 420.

It should be mentioned that it is essential when producing the cavities according to the second exemplary embodiment that protrusions 470 of tool 400 are adjusted to the initially produced thin layer areas on front side 440 of substrate 420.

For controlling the etching process, the etching conditions may be adjusted with decreasing distance between the tool and the substrate or during penetration of the protrusion into the substrate. It is conceivable, for example, to adjust the current or the concentration of the electrolyte solution to the etching progress.

To enable a material removal as uniform as possible across the entire substrate it is provided that the move of the tool toward the substrate is adjusted to the speed of the material removal so that there is no direct contact between the two electrodes. 

1. A method for electrochemical machining of a substrate using a conductive substrate (120, 420) and a conductive tool (100, 400), the tool having a surface structure (130), comprising: machining the substrate, starting with the tool, using an electrochemical etching process, and removing material from a surface of the substrate with aid of the etching process as a function of the surface structure of the tool, wherein the substrate and the tool are moved toward one another during the electrochemical etching process.
 2. The method as recited in claim 1, wherein the tool or the substrate remains locally stationary during the etching process, and wherein the tool is moved toward the substrate.
 3. The method as recited in claim 1, wherein material is removed from the substrate in a targeted manner with aid of the surface structure of the tool, and wherein the material is removed essentially perpendicularly to the substrate surface.
 4. The method as recited in claim 3, wherein the targeted material removal results in a separation of the substrate into a plurality of sub-substrates, and wherein the substrate is completely etched through according to its thickness.
 5. The method as recited in claim 1, wherein on a front side (140, 440) the substrate contains a plurality of sensor elements produced in or on the substrate, and wherein the material is removed from the substrate around the sensor elements or essentially on the rear side (150, 450) of the substrate opposite the sensor elements.
 6. The method as recited in claim 1, wherein the surface structure of the tool has protrusions and recesses, and wherein the recesses have a depth which corresponds at least to the thickness (160) of the substrate.
 7. The method as recited in claim 6, wherein, as material removal progresses, the tool is at least partially inserted into the substrate, and wherein the protrusions are inserted into the holes in the substrate produced by the material removal.
 8. The method as recited in claim 6, wherein at least one of the current and the concentration of the electrolyte solution are varied as a function of the distance of the tool from the substrate, and wherein the distance from the recess of the tool to the substrate surface is taken into account.
 9. The method as recited in claim 1, wherein the substrate represents a first electrode and the tool represents a second electrode for the electrochemical etching process, and wherein, during the etching process, direct contact between the substrate and the tool is avoided.
 10. A device for electrochemical machining of a substrate according to a method recited in claim 1, comprising: a conductive substrate (120, 420) and a conductive tool (100, 400), the tool having a surface structure (130), wherein the substrate is machined, starting with the tool, with aid of an electrochemical etching process, and material is removed from the surface of the substrate with aid of the etching process as a function of the surface structure of the tool, the device further comprising moving means for moving the substrate and the tool toward one another during the electrochemical etching process. 